A generator has been designed and constructed for creating electrical energy downhole in an oil well. The generator is driven with a progressing cavity motor as opposed to more classical methods, such as turbines. The progressing cavity motor is mechanically linked to the generator with a semi-rigid shaft. This shaft, referred to as a “flex shaft” is rigid enough to transmit a required amount of torque yet flexible enough to accommodate the eccentric neutation of the progressing cavity motor. The flex shaft in turn drives an electrical generator generally comprised of permanent magnets rotating about or within windings of an electrically conductive material such as copper wire. This results in the creation of an electrical charge capable of producing enough current to sustain electrical downhole instrumentation or other electrical devices. Further details regarding this generator are disclosed in Ser. No. 12/167,003 filed Jul. 2, 2008.
For a plurality of reasons, drilling fluid is pumped through the tubular string containing one or more drill collars from a pump located on the surface. A portion of this fluid is forced through the progressing cavity motor (pcm) located within a drill collar as the fluid travels downhole to pass to the drilling bit and return to the surface. The rotational speed of the pcm is directly proportional to the amount of fluid passing through the pcm. Under normal operations, this proportional amount is a minor portion of the total flow being supplied by the surface pump and passing through the drill collar.
In the process of drilling, the drilling mud may be pumped over a fairly wide flow range. This flow range may be 200 gallons per minute (gpm), up to and including 600 gpm. The output from the motor, however, desirably is a constant value. Flow through the pcm may be as much as 80 gpm or more.
While various designs exist for regulating fluid flow and pressure, this system modulates internal flow of drilling fluid within the motor. Substantially different yet related devices are taught in U.S. Pat. Nos. 3,974,876; 5,282,490; 5,301,713; 5,431,183; 6,053,196, and 6,129,112.
The disadvantage of the prior art is overcome by the present invention, an improved flow regulator for downhole pcm is hereinafter disclosed.